The present invention is directed to a gas sensor array for detecting individual gas constituents in a gas mixture. The array is composed of a plurality of individual sensor elements, which include semiconductive oxides, wherein the individual sensor elements are respectively applied on an electrically non-conductive substrate and wherein the array is provided with a contact electrode arrangement for measuring the electrical conductivity. In addition, the array includes a heating arrangement for heating to a given predetermined operational temperature, a protective sheath, which will protect the array against external mechanical influences, and a fastening base are also provided. The individual sensor elements have prescribed, individual operating temperatures allocated to them and the combinations between the respective sensor signals are formed for detecting the individual gas constituents, and these combinations are supplied to a processing unit.
Two proposals have been disclosed for selectively detecting and quantifying individual constituents in a gas mixture of chemically different gases. One of these proposals is directed to what is referred to as analysis equipment, wherein, for example, the employment are provided for quadripole mass spectroscopy or "FTIR". These relatively involved apparatus have the required suitability for measuring jobs at testing stands, such as, for example, motor testing stands and gas measuring stations. In the field of what is referred to as a low-cost apparatus that can be employed for monitoring jobs, it has also been proposed to employ gas sensors on the basis of heated tubes of semiconductive SiO.sub.2, which is provided with different precious metal dopings in order to obtain the selectivity of the sensor for a specific gas by projection. See, for example, an article by J. Watson and A. Price, Proc. IEEE, Vol. 66, 1978, p. 1670, which article is directed to an investigation of the selectivity of such sensors with respect to CO and to CH.sub.4.
These latter sensors have high transverse sensitivities, for example they are generally sensitive not only for the gas to be detected but also other gases. Given such sensors for reducing gases on the basis of SnO.sub.2, for example, the sensor with the basic material SnO.sub.2 is also O.sub.2 -sensitive, for example, these sensors for reducing gases also react to O.sub.2. Evaluation methods based on the principle of a pattern recognition can only be conditionally implemented with these sensors, since the individual sensors of an appertaining array do not generally comprise the stability required for this purpose. The problems that occur are based on the drift of the sensor signal and on unit scatter. In this respect, see a portion of a book by S. R. Morrison, Chemical Sensing with Solid State Devices, Academic Press, New York, 1989, Chapter 13.1.2.
Similarly constituted problems also occur given other standard sensor materials, such as, for example, Fe.sub.2 O.sub.3, TiO.sub.2 and, in particular, ZnO.